Hi Yaddek,
Thanks for posting in the community. We are happy to help you.
Once you convert a personal form to a group form (move a personal form to a group), you can't convert it back. Generally, this won't cause Excel file issues.
According to your description, I suggest you use another browser or use the InPrivate browser window to access the form again. Check if the problem still occurs.
If it still occurs, I would like to confirm if you have tried the function "Sync all responses to a new workbook".
- If not, I suggest you use this function to sync all responses to a new workbook, and then check again.
- If you have already tried, but the problem still occurs, it is likely caused by the server. To troubleshoot it further, I suggest you report this problem to your tenant admin or IT team and have them raise a support ticket via Microsoft 365 Admin Center> Support> New service request. That support team there will have the correct channel and resources to help you investigate more and find what exactly the reason has caused this problem at the backend.
Sorry for the inconvenience that happened to you. Appreciate your understanding and patience.
Sincerely,
George | Microsoft Community Moderator